In a wavelength-multiplexed optical signal treated in optical fiber communication, optical signals are orderly arranged according to a wavelength grid defined in an international telecommunication union telecommunication standardization sector (ITU-T) G.692 and are managed by channel numbers. General optical fiber communication, for example, is disclosed in Patent Literatures 1, 2 and the like.
However, in recent years, in optical fiber communication, an increase in a line demand is significant and higher-density multiplexing of optical signals is required. For example, it is proposed to perform large capacity transmission by multiplexing optical signals with high density to a limitation of frequency utilization efficiency by means of a multi-level modulation technology, a wavelength multiplexing technology, a spectrum control technology and the like.
In such high-density multiplexing transmission, with the development of a control technology of transmission waveforms of optical signals and a separation technology due to a digital computation of optical reception signals, a flexible grid, in which optical signals having mutually different bit rates and modulation schemes are transmitted with high density without depending on a wavelength grid, is introduced. Moreover, with the development of an optical wavelength control technology and an optical modulation technology, a multicarrier/super-channel technology, in which one line is transmitted through a plurality of spectrums is performed, is also applied.